JPH1180461A - Resin composition for splash guard - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a resin composition for a splash guard having an excellent formability and sound-proofing properties. SOLUTION: A resin composition comprised of 25-70 wt.% of a low density ethylene-based elastomer having less than 0.88 g/cm<3> density, 5-45 wt.% of a high density polyethylene-based resin having less than 0.5 melt index, and 10-50 wt.% of a filler is heat kneaded, and extruded to form a thin sheet product. The sheet is molded by vacuum and/or pressure forming or stamping molding prior to being cooled and hardened to obtain a splash guard having an excellent sound-proofing properties.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin composition for splash guard, and more particularly to a resin composition having excellent moldability and soundproofing.

[0002]

2. Description of the Related Art Conventionally, a resin splash guard is provided in a wheel housing facing a wheel of an automobile body. This is to prevent splashes and mud splashing up when the vehicle runs on the body, and to prevent the mud from directly hitting the body side, and is formed in an arch shape along the wheel housing. A resin plate having a thickness of several millimeters is drawn and formed by vacuum forming or the like, and attached to the body with a screw grommet, clip, or the like. The most reasonable and general method for forming this type of splash guard is to extrude a heated and molten resin composition into a sheet having a constant thickness by a sheet extruder, and to apply vacuum / air pressure before the sheet is cooled and solidified. This is a method of obtaining a required molded shape by molding or the like (by pressing a resin sheet against a molding die). The rationality of this molding method is that the sheet can be cooled once after extruding the sheet, then re-heated to the next step and then re-heated to form the sheet with fewer steps and energy efficient compared to the method of molding. is there.

In this type of splash guard, noise reduction has conventionally been a problem. Splashes and pebbles splash on an elastic, hard (thin) plate-like splash guard as the car travels, causing the splash guard to vibrate. May be transmitted and cause discomfort. A first conventional method for reducing this noise is to integrate various types of sound absorbing materials and sound absorbing structures on a splash guard. For example,
No. 73683, No. 57-141175, No. 5
7-133478 and JP-A-58-218777. Even if these could improve the noise reduction effect, the configuration of the splash guard would be complicated, leading to an increase in weight and manufacturing cost. A second method for reducing noise is to make the resin composition of the splash guard itself have strong vibration damping. Tokuhei 5-
39974 is an example. In this case, even if splashes or pebbles splash on the splash guard, there is an effect that vibration of the splash guard is small (attenuates quickly) and noise is reduced. Moreover, since the configuration of the splash guard is not complicated, it does not easily lead to an increase in weight and manufacturing cost.

[0004] However, such a resin composition greatly imposes limitations on the molding process and molding conditions of the splash guard. Since the splash guard for automobiles is a product having a complicated shape and requiring deep drawing, at least the conditions for extruding the sheet (especially for vacuum and / or pressure forming or stamping before the sheet is cooled and solidified) are required. The following are required: (1) Stretching conditions The resin sheet immediately after being extruded has sufficient stretchability. Preferably, the elongation of the resin at the time of melting is 200% or more. (2) Elastic condition The extruded resin sheet must have sufficient elasticity. Preferably, immediately after being discharged from the die lip, the thickness of the resin sheet increases to about 1.3 to 1.5 times the lip width due to elastic aftereffect. (3) Tension condition The extruded resin sheet generates a certain tension or more with respect to stretching. (4) Tension change rate condition The change in the tension should be as small as possible with respect to the change in the sheet take-up speed when the extruded resin sheet is taken out. If the conditions (1) to (3) are not satisfied among these conditions, the stretching of the resin sheet does not proceed smoothly, the sheet is likely to be uneven in thickness or torn, and is not suitable for forming a complicated shape. If the condition (2) is not satisfied, it is difficult to adjust the thickness of the resin sheet, and the thickness of the resin sheet tends to be uneven. If (4) is not satisfied, the neck-in amount of the resin sheet (the amount of shrinkage in the width direction of the sheet from the time when the sheet is extruded from the die lip to the time when the sheet enters between the molds) changes during the sheet take-off process. This is not preferable for vacuum molding, pressure molding, and stamp molding.

On the other hand, from the necessity of noise reduction, in a resin composition for splash guard, it is common to improve a soundproofing property (vibration damping property) by mixing a considerable amount of a filler with a base resin ( For example, the aforementioned Japanese Patent Publication No. 5-39974
issue). When the amount of the filler is reduced, the noise reduction effect is also reduced. However, the resin composition containing a large amount of the filler causes a decrease in stretchability of the sheet and a tension for stretching, so-called drawdown is remarkable, and a large size and a large size are obtained. A molded article having an area could not be obtained.

[0006]

Heretofore, there has been no resin composition satisfying the above-mentioned conditions (1) to (4) for molding a splash guard and further having excellent soundproofing properties. The present invention solves the above problems, and provides a resin composition having excellent moldability and soundproofing properties for use as a splash guard.

[0007]

Means of the present invention for solving the problems is to heat and knead the raw resin and extrude it into a sheet,
A resin composition for a splash guard obtained by vacuum and / or pressure forming or stamping before the sheet is cooled and solidified, and (A) a density of 0.88 g / cm ³
Density less than ethylene-based elastomer 25-70% by weight
(B) 5-45% by weight of a high-density polyethylene resin having a melt index value of less than 0.5, and (C) a filler 10
To 50% by weight of the resin composition for splash guard. The component (A) in the resin composition of the present invention is blended to enhance vibration damping. The component (A) is a flexible composition having many branches at the molecular structure level, and gives the splash guard a property that vibration is hardly transmitted (fast attenuation) even when it is hit by pebbles or the like. 0.8 density
If it exceeds 8 g / cm ³ , or if the amount is not sufficient, the effect of damping the vibration is reduced. The component (B) of the resin composition of the present invention is blended in order to maintain the moldability during vacuum and / or pressure forming before the sheet is cooled and solidified by heating and mixing the raw resin and extruding the sheet. You.
When the amount of the component (B) is insufficient or when the melt index value is 0.5 or more, the extruded sheet drops and the drawdown becomes large, so that the sheet cannot be stretched between the molds. Further, the component (B) needs to be blended for adjusting the neck-in amount and the swell amount suitable for molding the splash guard. The component (C) increases the vibration damping property as the blending amount increases. It is preferable to add 10% by weight or more.

[0008]

(Example) (A) Component: Low-density ethylene-based elastomer manufactured by Dow Chemical Company, trade name: Engage 8180, density: 0.86 g / cm ³ ) 30% by weight (B) Component: Asahi Kasei Kogyo High-density polyethylene resin manufactured by Co., Ltd. (trade name: HDPE-B870, density: 0.95 g / cm ³ , melt index value: 0.3) 40% by weight Component (C): 30% by weight calcium carbonate

FIG. 1 shows a molding apparatus for molding a splash guard from a resin composition. A plunger 2 is provided in the cylinder 1 so as to be movable in the axial direction, and the cylinder 1 and the plunger 2 constitute an accumulator head 3. An extruder 5 having a screw 4 is attached to the head of the cylinder 1, and a guide hole 5 </ b> A formed in the extruder 5 communicates with a storage hole 3 </ b> B formed in the cylinder 1. An operating cylinder (not shown) is provided at the upper end of the plunger 2 via a shaft portion 2a. By operating the operating cylinder, the plunger 2 can be forcibly moved in the axial direction. It is configured. At the lower end of the cylinder 1, a T die 6 having a molten resin discharge port 6a is attached.
Below the die 6, a sheet thickness adjusting section 8 for pulling down and stretching the resin sheet 7 discharged from the melt discharge port 6a is provided. The sheet thickness adjusting unit 8 is configured so that the chuck unit 11 can be moved up and down by the up and down movement of the rod 10 of the sheet thickness cylinder 9 to perform the stretching operation. A split mold portion 22 including a first mold 20 and a second mold 21 is disposed below the T-die 6 while holding the sheet thickness adjusting portion 8 therebetween. A female mold 20a is formed in the second mold 20 and a male mold 21a and the air discharge port 2 are formed in the second mold 21.
1b is formed. A compressed air source 23 such as a compressor is connected to the air discharge port 21b. The compressed air source 23 is connected to the control unit 24, and the sheet thickness cylinder 9 is also connected to the control unit 24. , The operation of which is controlled.

In this state, when the molten resin is stored in the storage hole 3B of the accumulator head 3 by the screw 4 of the extruder 5, the plunger 2 rises upward from the state shown in FIG. When the required amount of molten resin as a raw material is stored in the storage hole 3B, the plunger 2 is pushed down through an operating cylinder (not shown), and the molten resin discharge sheet 6 forms a molten resin sheet 7 from the molten resin discharge port 6a. Injected into. The resin sheet 7 by the above-mentioned injection is melted and discharged 6a.
Simultaneously, the rod 10 of the cylinder 9 for sheet thickness of the sheet thickness adjusting section 8 rises upward, and the chuck section 11 closes to chuck the lower end of the resin sheet 7. At the same time as this chuck operation is completed,
Since the rod 10 is lowered, the resin sheet 7 is extended downward to have a desired thickness, and is in a state corresponding to the female mold 20 a of the first mold 20. In the above-described state, the second mold 21 is joined to the first mold 20 via a cylinder (not shown), and the female mold 20a and the male mold 21a are tightly fitted with the resin sheet 7 held therebetween, and at the same time, the compressed air source is The compressed air from 23 is discharged to the resin sheet 7 and the skin 25a through the air discharge holes 21b, and the resin sheet 7 is formed by compression molding. In the forming apparatus shown in FIG. 1, it was extruded into a sheet, and was compressed and formed before being cooled and solidified. in this case,
The resin temperature is set to 200 to 220 ° C. inside the sheet, the discharge hole thickness of the molten resin is set to 1.5 mm, and the take-up speed of the resin sheet is set to 0.
The thickness of the sheet was adjusted by changing the thickness at a rate of ~ 300 m / s, and the drawn sheet was pressure-formed at a pressure of 4 kg / cm ² .

[0011]

The resin compositions of the examples were evaluated from the viewpoint of moldability and soundproofing, and good results were obtained. Regarding the moldability, the effects were confirmed in the following four points. The drawdown, which indicates the ease of dripping of the extruded sheet, was small and good. The uneven thickness showing the thickness variation of the extruded and stretched resin sheet was small and good evaluation. There was no tear during stretching or molding of the resin sheet. The resin sheet extruded from the discharge hole 6a is
The neck-in, which shows the contraction rate of the sheet width before entering 2,
The evaluation was small and good. The evaluation of soundproofing was performed by the device 30 shown in FIG. FIG. 2 shows a pendulum 34 composed of a steel ball 35 having a mass of 250 g connected to the tip of a thin string having a length of 200 mm with respect to a test piece 31 (molded product) mounted on a support 32 with a locking member 33. From the horizontal position, and hit the test piece end. At this time, the noise generated by the impact of the pendulum is simultaneously detected by the sound collector 36, and the vibration of the test piece is simultaneously detected by the acceleration detector 37, and is recorded on a recorder (not shown). The small absolute value of the initial noise and the rapid vibration damping were evaluated as having excellent soundproofing. FIG. 3 shows a measurement example of vibration damping. The effect was confirmed by comparing the example (a) of the present invention having good soundproofing properties with the example (b) having poor soundproofing properties.

[Brief description of the drawings]

FIG. 1 shows a molding method (molding machine) suitable for the present invention.

FIG. 2 shows a soundproofing evaluation device.

FIG. 3 shows a measurement example of a vibration damping state.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Cylinder 2 ... Plunger 2a ... Shaft part 3 ... Accumulator head 3B ... Storage hole 4 ... Screw 5 ... Extruder 5A ... Guide hole 6 ... T die 6a ··· Molten resin discharge hole 7 ··· Resin sheet 8 ··· Wall thickness adjusting section 9 ··· Cylinder 10 ··· Rod 11 ··· Chuck section 20 ··· First die 20a. ... second mold 21b ... female mold 23 ... compressed air source 24 ... control unit 30 ... soundproofing evaluation device 31 ... test piece 32 ... support 33 ... Stopper 34 ... Pendulum 35 ... Steel ball 36 ... Sound collector 37 ... Acceleration detector

Claims (1)

[Claims] 1. A resin composition for a splash guard obtained by heating and kneading a raw material resin, extruding it into a sheet, and vacuum and / or pressure forming or stamp forming before the sheet is cooled and solidified, wherein (A) Density 0.88g /
Density less than cm ³ Ethylene elastomer 25-70
A splash guard comprising (B) 5 to 45% by weight of a high-density polyethylene resin having a melt index value of less than 0.5, and (C) 10 to 50% by weight of a filler. Resin composition.